Molecular Identification of a Densovirus in Healthy and Diseased <b><i>Zophobas morio</i></b> (Coleoptera, Tenebrionidae)

Abstract

Zophobas morio is a tropical darkling beetle which is widely exploited for commercial large-scale insect growing. Outbreaks of a disease may occur causing total devastation of cultures. In the present paper, samples of diseased Z. morio were obtained and used for establishment of a laboratory model as they were found infective to the larvae of the same insect species from another source. It took about 1 month to develop symptoms of acute disease in mid-age larvae and about twice as much when younger larvae were used for infection. Affected larvae perished quickly, and within several days up to 90-100% of the colony could perish. Both in healthy and diseased larvae a virus was detected using PCR with degenerate primers specific for a gene coding for a nonstructural protein (ORF3). The sequenced gene fragment (Genbank accession #MN732869) confirmed allocation of the virus to Densoviridae, with maximal similarity of 97.2% to Blatella germanica densovirus-like virus (#JQ320376) and 66.2% to B. germanica densovirus (#AY189948). Genomic DNA samples of Z. morio larvae from an independent colony devoid of symptoms of a disease were also positive for this virus with a slightly different (99.7% sequence similarity to the former sequence of the Z. morio densovirus) genotype (#MN732870).

A Systematic Review on Viruses in Mass-Reared Edible Insect Species

“…Viruses that pose the highest risk for the collapse of mass insect rearing systems are those causing acute and high mortality because they can decimate commercial mass farms or entire colonies within a few days [44,88,100,258]. Another threat for edible insect producers are viruses that do not cause mortality but bring about a drastic decline in growth in the juvenile stages and in adult reproductive performance, with total collapse of the colony taking longer [190,204].…”

“…Little information is available on viral diseases in the super mealworm, with only two reports available to date on virus infection in Z. morio larvae [99,100]. The first refers to the collapse of a Z. morio colony in Hungary, where sudden large losses (80-90%) of Z. morio larvae were observed by a breeder in Budapest.…”

“…Diagnostic methods detected densovirus in colony larvae but no further identification was performed [99]. Tokarev and colleagues [100] reported isolation of a densovirus in Z. morio larvae cultured in Russia; in one month, middle-aged larvae developed symptoms of acute disease affecting the locomotion system, inducing swirling, rolling and chaotic wandering of larvae, and within several days, up to 90-100% of the colony had died. Prior to death the larvae showed no morphological changes but after death the cadavers blackened quickly, were more intensively stained, and the inner content was partially liquefied.…”

“…Prior to death the larvae showed no morphological changes but after death the cadavers blackened quickly, were more intensively stained, and the inner content was partially liquefied. Through biomolecular techniques the virus was attributed to Densoviridae, with maximal similarity to two Blatella germanica densovirus-like isolates from the bat [100]. One of these latter viruses could develop within vertebrate tissue [101].…”

“…One of these latter viruses could develop within vertebrate tissue [101]. Thus, the hazard of vertebrate host infection with insect densoviruses cannot be excluded [100].…”